Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.72   11.591%   $75.5694   $75.57   $75.55   $75.60  
  Purchase #2 $222.31   3.695%   $230.5244   $230.52   $230.50   $230.50  
  Purchase #3 $6.77   6.161%   $7.1871   $7.19   $7.20   $7.20  
  Purchase #4 $25.60   13.641%   $29.0921   $29.09   $29.10   $29.10  
  Purchase #5 $196.52   12.803%   $221.6805   $221.68   $221.70   $221.70  
  Purchase #6 $46.47   9.640%   $50.9497   $50.95   $50.95   $50.90  
  Purchase #7 $140.54   7.701%   $151.363   $151.36   $151.35   $151.40  
  7 purchase totals = $705.93       $766.3662   $766.36   $766.35   $766.40